Method of making thin metal sheets



June 10', 1958 F, c. KELLEY 2,837,817

METHOD 0F MAK'TNG THIN METAL SHEETS /fa/z, ame armar@ jane:

TGR/VE YS i Floyd C. Kelley,

METHOD on MAKING THIN METAL srrEErs Schenectady, N. Y., assignonrby mesne assignments, to the United States of America as represented by the Secretary of the Navy Application August 18, 1955, Serial No. 529,368 7 claims. (ci. zei-42,4)

metal foils. However, it is particularly difficult to obtain thin foils of molybdenum or tungsten for cathode fabrication which are free from cracks and imperfection and itis also difficult to avoid further cracks or imperfections when the thin molybdenum lor tungsten foil is shaped intoa cathode cup. l

Accordingly, it is the primary object of the present invention to provide a method of preparing sheets of metal foil which are free from cracks or imperfections.

. It is a further object to provide a method of preparing sheets of molybdenum orA tungsten having a thickness of 0.1 to 0.2/ mil. Y

,It is another object to provide a method of preparing cathode cups free from cracks and imperfections consisting of molybdenum or tungsten foil having a thickness of 0.1 to 0.2 mil. Y

.'In accordance with the present invention, there Vis provided a method of preparing thin molybdenum and tungsten foil which comprises the steps of cleaning one Vsurface of a thin sheet of the molybdenum or tungsten and one surface of a thicker larger sheet of iron:and then placing the clean surface of the molybdenum or tungsten sheet upon and within the periphery of the clean surface of the iron sheet. A sheet of stainless steel which is substantially equal in dimension to the iron sheet is placed upon the other surface of the molybdenum -or tungsten sheet. A plurality of spaced spot welds between the iron and the stainless steel is made at the periphery to form a compact comprising the stainless steel, either molyb denum or tungsten and the iron. The compact is heated in an enert gas atmosphere to a temperature of about 80G-900 C. and then the heated compact is rolled ,to reduce its total original thickness by about 35 to 45% and to iirmly bond the molybdenum or tungsten to the iron. The reduced compact is further rolled to reduce its total original thickness by about 50-60% and to free the stainless steel from the Vcompact leaving either a tungsten or molybdenum clad iron strip. The molybdenum clad iron strip may be further cold rolled to a chosen thickness after which the strip is annealed. The iron may be removed from the strip by dissolution or otherV chemical means to provide the thin molybdenum film which is free from cracks and imperfections. lron is solublein dilute sulphuric` acid and hydrofluoric acid but molybdenum is insoluble in hydroliuoric and dilute sulphuric acids and the tungsten is Vinsoluble in hydrouoric acid so that a States Patent O i a cleaned surface of a relatively thin slab of molybdenum,

choice of the proper acids may be made to dissolve the iron without affecting the molybdenum or tungsten.

Also in acordance with the present 'invention there is provided a method of preparing a cathode cup consisting either of a thin foil of either molybdenum or tungsten which comprises the steps of cleaning one surface of aY clean sheet of molybdenum or tungsten havinga thickness of from 1 to 4 mils and one surface of a larger sheet of iron having a thickness of 1,652 to V32 inch. The cleaned surface of the molybdenum or tungsten is placed upon the cleaned surface of the iron and within the periphery thereof. A sheet of stainless steel which is substantially equal in dimensions to the iron sheet is placed upon the` other surface of themolybdenum sheet. A plurality of spot welds is made between the iron and stainless steel at the periphery to form a compact of the stainless steel, the molybdenum or tungsten and the iron. The compact is heated in a hydrogen atmosphere to a temperature of SOO-900 C. and is rolled to reduce its total original thickness by about 35-45 and to iirmly bond the molybdenum or tungsten to the iron. A further rolling is then made with said reduced compact to reduce its total originalthickness by 50 to 60%l and to free the stainless steel,l from the compact, leaving la molybdenum or tungsten clad iron strip. A further cold rolling ofthe molybdenum strip may be made to a total thickness of about 5 mils. after which the strip is annealed. The strip is then shaped into a cup or cup-like structure andthe iron is removed therefrom by chemical means, thereby providing a molybdenum cup-like structure having a thickness of 0.1 toV 0.2 mil.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description. A,

The single figure illustrates a method in accordance 'with this invention.

Generally speaking, the process of the present inven tion is performed by placing a clean surface of a relatively thick slab of metal, preferably iron, in contact withl or tungsten. The surfaces may be cleaned readily bythe conventional method of gritblasting and subsequent wire brushing. A sheet of stainless steel which is not'cleaned on either surface is placed upon the uncleaned surfaceof the molybdenum or tungsten. The resulting sandwichv of stainless steel molybdenum or tungsten and iron isy then spot welded around the periphery at intervals to form a compact. The molybdenum or tungsten sheet is in-` tentionally made narrower in both -dimensions than either the iron or the steel sheets which are substantiallyequalin thickness and dimensions 'so that the spot welds around the periphery are made between the iron andthe steel;

The lwelded compact is then placed in a hydrogen furnace and heated to 800 to 900 C. A hydrogen furnace is selected since it furnishes an inert and a reducing atmosphere so that the tungsten or molybdenum, iron andy steel are not subjected to any deleterious chemical action during the heating. Although a hydrogenatmo's` phere is preferable, it may be replaced by'anotherzinert gas atmosphere such as of nitrogen or one of the noble gases. The compact is then given a heavy reduction yby.V passing it between the pressure rolls of a rolling mill. The first pass through the rolls may reducethe thickness of the compact by about 40% and will also'cause the molybdenum or tungsten to be irmly bonded to the'iron. A second pass reduces the original thickness about 50 to 60% and due to the elongation of the metal sheets and the cooling thereof, a rupture of the spot welds will take placeand thel stainless steel is freed from the compact leaving a molybdenum or tungstenrclad iron strip. The

Patented Jane v1o, 1958,

t 3 Y latter may be cold rolled to further reduce its thickness after which it is annealed.` Such annealing may be any method well known in the art. After the annealing, it has been found that the molybdenum or tungsten is in substantially perfect condition and shows no cracks or imperfection.

The annealed molybdenum or iron strip` may be treated to remove the iron therefrom to provide thin foil sheets of molybdenum and tungsten. Since iron is soluble in hydrouoric acid and dilute sulphuric acid and since molybdenum is insoluble in both of these acids and tungsten Yis insoluble in hydrofluoric acid, in the case of the molybdenum clad iron strip, the iron may be removed by submersion in a solution of dilute sulphuric acid or hydrouoric acid. In the case of the tungsten clad iron strip, the iron may be removed by submersion of the strip in a solution of hydroliuo'ric acid.

To make cathod'es consisting of thin films `of molybdenum or tungsten, either themolybdenum clad iron or tungsten clad iron strip is first shaped into the form of a cup before it is submerged into the iron dissolving acid. After'the iron has been dissolved, there remains a cathode cup-like structure consisting either of molybdenum or tungsten. Since the molybdenum or tungsten provided on the strip is substantially free of cracks or imperfections and since the shaping operation of the strip into a cup-like structure does not cause cracks Vand imperfections, it is to be seen, that a cathode consisting of a substantially perfect -oil of molybdenum or tungsten is provi-ded by the present invention.

Typical quantities used to provide the present invention may be seen in the following example:

First rolling: Reduction kofv 35 to 45% of ori-gina] thickness.

Second rolling Reduction of 50 to 60% of original thick- Third rolling: Reduction kto a total thickness of about 5 mil. Dissolution of iron leaves a molybdenum or tungsten foil of 0.1 to 0.2 mil thickness.

In a precise embodiment of the present invention, the beginning materials were 1/16 iron sheet, 2.5 mil molybdenum or tungsten sheet and 1/16 stainless sheet, as described above. Of course, thicker sheets may be used to produce other filial desired thicknesses.

Obviously many modications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the'scope of the appended claims the invention may be practiced otherwise than as specifically described.

I claim:

A1. A method of lpreparing a thin foil of a metal selected from the group consisting of molybdenum and tungsten which comprises the steps of cleaning one surface of a thin sheet of said metal and one surface of a thicker larger sheet of iron; placing the cleaned surface of said metal sheet against andwithin the periphery of the cleaned surface of said iron sheet; placing a sheet of uncleaned stainless steel which is substantially equal in dimensions to said iron sheet against the uncleaned surface of said metal sheet; making a plurality of spaced spot welds between said iron and said stainless steel at said periphery toform a compact comprising said stainl'ess steel, said metal, and said iron; heating said compact in a noncorrosive atmosphere to a temperature of 800 C. to 900 C.; rolling said heat compact to reduce its total original 'thicknessby about 35 to 45% and to firmly bond said metal to said iron; further rolling said heated compact to further reduce its total original thickness by 50 to 60% and to free said stainless steel from said compact leaving a laminate of said metal and said iron; cold rolling said laminate to a chosen thickness; annealing said laminate; and then dissolving said iron away from said laminate whereby there is obtained a thin foil of said metal.

2. A method of preparing thin molybdenum foil which comprises the steps of both cleaning one surface of a thin sheet of molybdenum and one surface of a thicker larger sheet of iron; placing the cleaned surface of said molybdenum sheet against and within the periphery of the cleaned surface of said iron sheet; placing a sheet of uncleaned stainless steel which is substantially equal in dimensions to said iron sheet against the uncleaned surface of said molybdenum sheet; making a plurality of spaced spot welds between said iro-n and said stainless steel at said periphery to form a compact of said stainless steel, said molybdenum, and said iron; heating said compact in a hydrogen atmosphere to a temperature of 800 to 900 C.; rolling said heated compact to reduce its total original thickness by about 35% to 45% and to firmly bond said molybdenum to said iron; further rolling said reduced heated compact to reduce its total original thickness by about 50% to 60% and to free said stainless steel from said compact leaving a molybdenum clad iron strip; cold rolling said molybdenum clad iron strip to a chosen thickness; annealing said strip; and then removing the iron from said strip by dissolution thereof in a material selected from the group consisting of a hydroliuoric acid solution and a dilute sulphuric acid solution.

3. A method of preparing thin molybdenum foil which comprises the steps of cleaning one surface of a thin sheet of molybdenum having a thickness of l to 4 mils and one surface of a larger sheet of iron having a thickness of Q2 to 5;(32 inch; placing the cleaned surface of said molybdenum sheet against and within the periphery of the cleaned surface of said iron sheet; placing a sheet of uncleaned stainless steel which is substantially equal in dimensions to said iron sheet against the uncleaned` surface of said molybdenum sheet; making a plurality of spaced spot welds between said iron and said stainless steel at said periphery to form a compact of said stainless steel, said molybdenum and said iron; heating said compact in a `hydrogen atmosphere to a temperature of 800 to 900 C.; rolling said heated compact to reduce its total original thickness by about 35% to 45% and to firmly bond said molybdenum to said iron; further rolling said reduced heated compact to reduce its total original thickness by 50% to 60% and to free said stainless steel from said compact leaving a molybdenum clad iron strip; cold rolling said molybdenum clad iron strip to a total thickness of about 5 mils; annealing said strip; and then removing said iron therefrom by dissolution thereof in a material selected from the group consisting of a hydrouoric acid solution and a dilute sulphuric acid solution whereby there is provided a molybdenum foil having a thickness of 0.1 to 0.2 mil.

4. A method of preparing a cathode comprising a thin molybdenum foil which comprises the steps of cleaning one surface of a sheet of molybdenum having a thickness of l to 4 mils and one surface of a larger sheet of iron having a thickness of 1,5;2 to 37,532 inch; placing the cleaned surface of said molybdenum sheet against and within the periphery of the cleaned surface of said iron sheet; placing a sheet of uncleaned stainless steel which is substantially equal in dimensions to said iron sheet against the uncleaned surface of said molybdenum sheet; making a plurality of spaced spot welds between said iron and said stainless steel at said periphery to form a compact of said stainless steel, said molybdenum, and said iron; heating said lcompact in a hydrogen atmosphere to a temperature Vof 800 to 900 C.; rolling said heated compact to reduce its total original thickness by about 35% to 45% and to firmly bond said molybdenum to said iron; further rolling sai-ii reduced heated compact to reduce its total original thickness to about 50 to 60% and to free said stainless steel from said compact leaving a molybdenum clad iron strip; cold rolling said molybdenum clad iron strip to a thickness of about mils; annealing said strip; forming said annealed strip into a cup-like structure; and then removing the iron from said cup-like structure by dissolution thereof in material selected from the group consisting of a hydrofluoric acid solution and a dilute sulphuric acid solution whereby there is provided a cathode of cup-like structure consisting of a molybdenum foil of one of 0.1 to 0.2 mil thickness.

5. A method of preparing thin tungsten foil which comprises the steps of cleaning one surface of a thin sheet of tungsten and one surface of a thicker larger sheet of iron; placing the cleaned surface of said tungsten sheet against and Within the periphery of the cleaned surface of said iron sheet; placing a sheet of unc-leaned stainless steel which is substantially equal in dimensions to said iron sheet against the uncleaned surface of said tungsten sheet; making a plurality of spaced spot welds between said iron and said stainless steel at said periphery to form a compact of said stainless steel, said tungsten, and said iron; heating said compact in a hydrogen atmosphere to a temperature of 800 to 900 C.; rolling said heated compact to reduce its total original'thickness by about 35% to 45% and to firmly bond said tungsten to said iron; further rolling said reduced heated compact to reduce its total original thickness by about 50% to 60% and to free said stainless steel from said compact leaving a tungsten clad iron strip; further cold rolling said tungsten clad iron strip to a chosen thickness; annealing said strip and then removing said iron from said strip by dissolution thereof in hydrouoric acid solution.

6. A method of preparing a thin tungsten foil which comprises the steps of cleaning one surface of a sheet of tungsten of 1 to 4 mils thickness and one surface of a larger sheet of iron having a thickness of 1,652 to 3/32 inch; placing the clean surface of said tungsten sheet against and within the periphery of the clean surface of said iron sheet; placing a sheet of uncleaned stainless steel which is substantially equal in area and thickness to said iron sheet against the uncleaned surface of said tungsten sheet; making a plurality of spaced spot welds between said iron and said stainless steel at said periphery to form a compact of said stainless steel, said tungsten and said iron; heating said compact in a hydrogen atmosphere to a temperature of 800 to 900 C. rolling said heated compact to reduce its total original thickness by about 35% to and to firmly bond said tungsten to said iron; further rolling said reduced heated compact to reduce its total original thickness by to 60% and to free said stainless steel from said compact leaving a tungsten clad iron strip; further cold rolling said tungsten clad iron strip to a thickness of about 5 mils; and then removing said iron from said strip by dissolution thereof in a solution of hydroiluoric acid whereby there is provided a tungsten foil having a thickness of 0.1 to 0.2 mil.

7. A method of preparing a cathode consisting of a thin tungsten foil which comprises the steps of cleaning one surface of a tungsten sheet having a thickness of 1 to 4 mils and one surface of a larger sheet of iron having a thickness of 1&2 to 5732 inch; placing the clean surface of said tungsten sheet against and within the periphery of the clean surface of said iron sheet; placing a sheet of uncleaned stainless steel which is substantially equal in dimensions to said iron sheet against the uncleaned surface of said tungsten sheet; making a plurality of spaced spot welds between said iron and said stainless steel at said periphery to form a compact of said stainless steel, said tungsten, and said iron; heating said compact in a hydrogen atmosphere to a temperature of 800 to 900 C.; rolling the heated compact to reduce said total original thickness by about 35% to 45% and to firmly bond said tungsten to said iron; further rolling said reduced heated compact to reduce its total original thickness by 50% to 60% and to free said stainless steel from said compact leaving a tungsten clad iron strip; further cold rolling said tungsten clad iron strip to a thickness of about 5 mils; annealing said strip; shaping said annealed strip to a cup-like structure;'and removing said iron therefrom by the dissolution thereof in a hydroiiuoric solution whereby there is provided a cup-like tungsten cathode consisting of a tungsten foil having a thickness of .1 to .2 mil.

References Cited in the le of this patent UNITED STATES PATENTS 827,696 Lewis July 31, 1906 1,610,225 Metcalf Dec. 7, 1926 1,886,615 Johnson Nov. 8, 1932 1,956,818 Acre May 1, 1934 1,981,915 Hormel Nov. 27, 1934 2,423,810 Goulding July 8, 1947 

